Method of making refrigerating apparatus



N v- 19 L. J. MANN 2,958,934

METHOD OF MAKING REFRIGERATING APPARATUS Filed Aug. 5, 1952 2Sheets-Sheet 1 4 INVENTOR.

Leonard J. Mann,

Nov. 8, 1960 L. J. MANN 2,958,934

METHOD OF MAKING REFRIGERATING APPARATUS Filed Aug. 5, 1952 2Sheets-Sheet 2 FIT JNVENTOR. Leonard J. Mann,

2,958,934 Patented Nov. 8, 1960 METHOD OF MAKING REFRIGERATING APPARATUSLeonard J. Mann, Dayton, Ohio, assignor to General Motors Corporation,Dayton, Ohio, a corporation of Delaware Filed Aug. '5, 1952, Ser. No.302,748

1 Claim. 01. 29-1572 This invention relates to refrigerating apparatusand more particularly to heat exchangers and the method. of making thesame.

This invention is particularly intended to utilize a process whereinapair of weldable metal sheets are roll welded together and wherein theone sheet is precoated with a stop-weld material in a definite patternso as to prevent the welding of the two sheets throughout the coatedarea whereby it is possible to separate the sheets throughout the coatedarea by the application of hydraulic pres sure between the sheets so asto form internal passages.

The pressure required for hydraulically dilating the passages in a rollwelded sheet metal heat exchanger are so great that it is essential tolimit the size of the passages thus formed and it is also essential tolimit the degree of expansion of even the smaller passages by means ofheavy protective plates or blocks placed on opposite sides of the sheetmetal during the process of dilating the passages. Due to the processused in forming the passages, the location of the passages variesconsiderably from one pair of plates to another and therefore it isimpractical, if not impossible, to use protective blocks which haverecesses corresponding to the final shape of the passages to be formed.This then complicates the problem of forming heat exchangers and thelike wherein some of the internal passages or chambers are larger thanothers. The high pressures required for di lating the smaller passagesand the irregularity in the pat tern of the smaller passages eachpresent different prob lems.

It is an object of this invention to provide a heat ex changer designand a method of making heat exchang ers which makes it possible tohydraulically dilate the relatively small fluid passages even thoughthey connect onto a relatively large header which could not be formed bydilating a portion of the roll welded sheets,

One object of this invention is to form the header separately from themain body of the heat exchanger and to weld the two together while themain body of the heat exchanger is still perfectly flat.

More particularly it is an object of this invention to provide a heatexchanger and a method of making the heat exchanger which makes itpossible to weld the header to the main body before the internalpassages of the heat exchanger body have been dilated.

Still another object of this invention is to provide an improved methodof manufacturing heat exchangers and the like wherein chambers ofdifierent sizes are formed by a process which does not requirestretching the metal forming the Walls of the larger chambers.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had'to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

In the drawings:

Figure 1 is a plan view showing a heat exchanger a sembly in anintermediate stage of manufacture just prior to the formation of thefluid passages and header chamber;

Figure 2 is a side elevational view of the structure shown in Figure 1on a slightly enlarged scale;

Figure 3 is a view similar to Figure 2 but showing the shape of the heatexchanger after the fluid passages have been dilated;

Figure 4 is a fragmentary plan view showing the relationship of theheader to the fluid passages after the dilation of the various fluidpassages and the header chamber;

Figure 5 is a vertical sectional view showing the plates which are usedfor limiting the extent of dilation;

Figure 6 is a fragmentary elevational view showing a modified headerconstruction;

Figure 7 is an end elevational view for illustrating the manner in whichthe header is formed;

Figure 8 is a vertical sectional view through the header in anintermediate stage of manufacture; and

Figure 9 is a view similar to Figure 8, but showing the manner in whichthe header is attached to the main body of the heat exchanger prior tothe dilation of the refrigerant passages.

Figure 1 of the drawings shows an illustrative forgewelded compositeplate 10 having stop-weld material 12 arranged in a pattern so as toestablish the location of predetermined passages within the plate. Theindividual sheets used for forge-welding are preferably made of .070"thick weldable bronze of the following specification:

Copper92-94% Iron-2. 1-2.6

Zinc substantially all the remainder Iron/ zinc minimum .30

Tensile strength 44,000 lbs. per sq. in. minimum Elongation-in 2 inches31% minimum Hardness Rockwell H 96-103 The above specification is merelyillustrative as any other type of weldable material such as copper,brass, or aluminum could be used in place of the bronze.

The sheets which are used in forming the main body of the heat exchangerare cut to approximately the same width as the width of the finalproduct but are approximately /3 shorter than the length of the finalproduct desired. As explained hereinabove stop-weld material 12 isapplied to the one sheet so as to prevent the adjacent shects fromadhering to oneanother at those places where the stop-weld coating ispresent. This stop-weld material maybe applied by printing, rolling,painting or spraying the stop-weld material in fluid or solid form. Inthis example, the stop-weld material is in the form of a watersuspension of colloidal graphite and sodium silicate which serves as abinder.

The one portion of the stop-weld material extends to one edge of theplates as indicated by the reference numeral 1-4. After the stop-weldcoating has beenplaced on the one sheet and another sheet laid thereonwith the coating then being disposed between the two sheets, the edgesof the two sheets are inert gas welded so as to hold them together inthe desired relationship and so asto prevent the admission of airbetween the sheets during the subsequent roll-forging or weldingoperation. The.

process to the same extent of the elongation of the sheets as they wererolled into one composite sheet. Several cold-rolling passes may followthe initial hot-rolling pass to bring the final composite sheet toapproximately the desired length. The final length in this example isabout 2.92 times the original. length. The thickness of the singlecomposite sheet is allowed to vary between .045 and .048 inch. Followingthe final rolling operation the composite sheet is annealed. The rollingand the annealing causes the line of separation between the two sheetsto disappear and recrystallization and grain growth extends across theformer line of separation so that the two sheets have been completelyforge-welded into one composite sheet except where stop-weld materialhas been provided.

The inert gas welded edges of the sheets are cut away so as to exposethe stop-weld material at the one end of the plate and at 14 and so asto form a product having straight, clean-cut edges with the finishedouter dimensions of all of the heat exchangers thus formed beingabsolutely uniform.

By inspection of the trimmed edges of the composite plate it is possibleto determine the area where the stop-weld material 14 extends to theedge of the sheet and at this point the sheets are mechanically forcedapart so as to make it possible to introduce fluid under pressure forseparating the sheets throughout the area covered by the stop-weldmaterial. However, before this separation or dilation of the sheets isundertaken a folded sheet member 16 is slipped over the one end of theplate 10 as best shown in Figures 1 and 2 and is inert gas welded to theplate 10 as indicated at 18. Since the plate member 10 is still aperfectly flat plate, it is a simple matter to provide a good weldedjoint between the members 10 and 16. The ends of the folded member 16are also inert gas welded so as to seal the same as indicated by thereference numeral 20.

After the element 16 has been properly secured to the element 10, theassembly is placed between a pair of heavy rigid plates or block members30 and 52. The plates or block members 30 and 32 may be held in a press(not shown) or otherwise held against separation so as to firmly gripthe edges of the plate 10. The members 30 and 32 are provided withspaced fiat surfaces 34 and 36, respectively, which overlie the mainbody of the plate 10 wherein the fluid passages are to be formed and arecut away as indicated at 38 and 40 so as to allow for dilation of thefolded plate 16 so as to form a header element 42. The depth and shapeof the cuts 38 and 40 are such that the dilation of the header isstopped before the walls of the header are stretched any appreciableamount. Since the folded plate portion 16 has not been produced by theroll-forging operation, all of these plates 16 may be made of exactlythe same size and shape with the result that all of the headers will beof the same shape and in the same relative location with respect to themain body of the heat exchanger.

After the heat exchanger assembly has been inserted between the blocks30 and 32, fluid under pressure is used for hydraulically dilating orexpanding all of the passages which are to be formed. The hydraulicpressure required for properly expanding the heat exchanger is 10,000pounds per square inch or higher. By using rigid flat surfaces forlimiting the expansion or dilation of the smaller passages, therupturing of the walls of the passages is prevented and the entire mainbody of the heat exchanger remains uniformly flat.

Experience shows that passages formed by hydraulically expanding thesame while the roll-forged plate is held between flat blocks haveuniformly flat top and bottom surfaces 48 which are particularlydesirable in refrigerant evaporators, for example. These flat surfacesprovide excellent contact for ice trays and other vessels which may beplaced on the surface of an evaporator.

By virtue of the fact that the passages are expanded by thesubstantially flat blocks rather than complex dies which have recessesexactly corresponding to the final outer contour of the entire heatexchanger, it is obvious that any unevenness in the location or lengthof the smaller fluid passages does not present any problem.

Upon completion of the dilating process the composite device may beremoved from between the heavy plates or blocks 30 and 32 and then bentinto any desired shape.

Although one specific example has been given it should be understoodthat the arrangement of the fluid passages as well as the types ofmaterials which are used could be varied. By virtue of the method usedin manufacturing the heat exchanger it is possible to weld the headersec tion to the main body of the heat exchanger at a time when the jointbetween the two may be easily made even though the final joint assumesmuch more intricate shape as indicated in Figure 4 of the drawing. Thus,as shown in Figure 4 of the drawing, the various passages formed in themain plate 10 extend up into the header in the finished form.

In Figures 6 through 9 of the drawing there is shown a modified type ofheader construction wherein the header 52 is formed by taking acylindrical tank like element 54 as shown in Figure 7 and crimping itadjacent one edge throughout its major length until it assumes a shapelike the dot-dash shape shown in Figure 7. The bottom end 56 of thecrimped portion is cut away so as to make it possible to insert aforge-welded heat exchanger element 60 between the flanges 62 of theheader 52. The main body of the heat exchanger element 60 may be madesimilar in every respect to the heat exchanger element 10 describedhereinabove.

The element 60 is assembled between the flanges 62 before any of thefluid passages are dilated whereby a straight flat seam is providedbetween the element 60 and the flanges 62. The flanges 62 then are inertgas welded or otherwise fused or brazed to the plate 60 so as to providean absolutely gas-tight joint between the flanges 62 and the outer wallsof the element 60. After the flanges of the header element 52 have beenproperly secured to the element 60, the assembly is placed between apair of blocks such as the blocks 30 and 32 which would be provided witha preformed cavity for receiving the header 52 so as to prevent anyfurther deformation of the header 52 during the process of dilating thefluid passages in the element 60. Fluid for dilating the passages in theelement 60 may be introduced through the conduit 64 which connects tothe header 52 as shown in Figure 6. Upon introduction of the dilatingfluid, preferably a liquid, the fluid passages 66 are formed in the mainbody member 60. It will be noted that in forming the passages 66 theflanges 62 are also reshaped and that the walls of the passages are flatsided. It is obvious that it would be much more diflicult to provide afluid tight welded joint between the header 52 and the main body 60 ofthe heat exchanger if the welding operation were to be performed afterthe fluid passages in the element 60 were dilated. By virtue of themethod and construction used in each of the above described heatexchangers it is obvious that the element which forms the header portionmay be made separately from the roll-forged body of the heat exchangerand that the connection between the header portion and the body portionmay be made before the final shaping of the fluid passages.

While the. form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, as may come within the scope of the claim whichfollows.

What is claimed is as follows:

The method of manufacturing heat exchangers and the like whereinchambers of dilferent sizes are formed without stretching the metalforming the walls of the larger of the chambers which comprises rollforging into one. composite sheet apair of metal sheets having stop 5weld material therebetween in the pattern of fluid passages some ofwhich extend to one edge of said sheets, forming a relatively largeheader chamber by folding a flat third sheet member over onto itself andslipping those fiat edges of the folded sheet member which are oppositethe fold over onto said one edge of said roll forged sheets while theouter sides of said rol-l forged sheets are still flat, inert gaswelding the edges of the folded sheet member to the roll forged sheets,inert gas welding the ends of the folded sheet member so as to seal thesame, dilating said passages and said header by subjecting the interiorof said passages and said header to a fluid pressure and limiting theextent of dilation by placing the header and composite sheet between apair of spaced confining dies having flat faces opposite said fluidpassages and having cuts opposite said header chamber, the depth andshape of said cuts being such that the dilation of the header chamber isstopped before the walls of the header are stretched any appreciableamount.

References Cited in the file of this patent UNITED STATES PATENTS Re.18,182 Booth Sept. 8, 1931 6 Holmes July 24, Evans Oct. 29, Litle May 7,Rosenqrist Aug. 6, Keig-hley Aug. 18, Hastings June 29, Sendzimir Aug.20, Booth Aug. 27, Nickolas Sept. 5, Davis Jan. 9, Hytte May 26, LongDec. 15, Grenell Sept. 28, Simmons Apr. 3, Heidorn July 31, Adams et a1.Oct. 9,

FOREIGN PATENTS Great Britain Mar. 27, Denmark Apr. 16,

